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The Adaptive Immune System of Haloferax volcanii

Department of Biology II, Ulm University, 89069 Ulm, Germany
School of Biomedical Sciences, Charles Sturt University, 2650 NSW, Australia
Author to whom correspondence should be addressed.
Academic Editors: Roger A. Garrett, Michael W. W. Adams and Hans-Peter Klenk
Life 2015, 5(1), 521-537;
Received: 9 December 2014 / Accepted: 3 February 2015 / Published: 16 February 2015
(This article belongs to the Special Issue Archaea: Evolution, Physiology, and Molecular Biology)
PDF [829 KB, uploaded 16 February 2015]


To fight off invading genetic elements, prokaryotes have developed an elaborate defence system that is both adaptable and heritable—the CRISPR-Cas system (CRISPR is short for: clustered regularly interspaced short palindromic repeats and Cas: CRISPR associated). Comprised of proteins and multiple small RNAs, this prokaryotic defence system is present in 90% of archaeal and 40% of bacterial species, and enables foreign intruders to be eliminated in a sequence-specific manner. There are three major types (I–III) and at least 14 subtypes of this system, with only some of the subtypes having been analysed in detail, and many aspects of the defence reaction remaining to be elucidated. Few archaeal examples have so far been analysed. Here we summarize the characteristics of the CRISPR-Cas system of Haloferax volcanii, an extremely halophilic archaeon originally isolated from the Dead Sea. It carries a single CRISPR-Cas system of type I-B, with a Cascade like complex composed of Cas proteins Cas5, Cas6b and Cas7. Cas6b is essential for CRISPR RNA (crRNA) maturation but is otherwise not required for the defence reaction. A systematic search revealed that six protospacer adjacent motif (PAM) sequences are recognised by the Haloferax defence system. For successful invader recognition, a non-contiguous seed sequence of 10 base-pairs between the crRNA and the invader is required. View Full-Text
Keywords: CRISPR-Cas; PAM; crRNA; Cas6; Cascade; archaea; Haloferax volcanii; type I-B CRISPR-Cas; PAM; crRNA; Cas6; Cascade; archaea; Haloferax volcanii; type I-B

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Maier, L.-K.; Dyall-Smith, M.; Marchfelder, A. The Adaptive Immune System of Haloferax volcanii. Life 2015, 5, 521-537.

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